Use this to convert transmissions .resume files from an old installation with different file hierarchy

replace_transmissions_resume_file_prefixes.py

from pathlib import Path

OLD = b"/old/downloads/dir/"
NEW = b"/new/downloads/dir/"

for fname in Path(".").glob("*.resume"):
    print(fname)
    with fname.open("rb") as f:
        data = f.read()

    count = 0
    while b':/mnt/downloads/' in data:
        count += 1

        offset_sep = data.find(b':' + OLD)
        offset_num = offset_sep - 1
        while data[offset_num-1:offset_num].isdigit():
            offset_num -= 1

        length = int(data[offset_num:offset_sep])
        path = data[offset_sep+1:offset_sep+1+length]
        assert path.startswith(OLD)

        head = data[:offset_num]
        tail = data[offset_sep+1+length:]
        path = path.replace(OLD, NEW)
        data = head + str(len(path)).encode() + b':' + path + tail

    print(count, "entries changed.")

    with fname.open("wb") as f:
        f.write(data)